1. Field of the Invention
The present invention relates to a microscope system, and more particularly to a microscope system such as a fluorescence microscope system provided with an illumination mechanism for illuminating a specimen.
2. Description of the Related Art
Generally, a microscope system of a Kohler illumination type is provided with a field stop function of illuminating a region to be observed on a specimen, the illuminated region being the same as the observation region. In this microscope system, a field stop is so adjusted as to illuminate the necessary part of the specimen in a field at a time of fluorescence observation and the necessary part of the specimen is observed. Thus, the other part of the specimen can be prevented from being deteriorated and bleaching out, due to the illumination of fluorescence light.
In addition, an observation method such as FRAP (Fluorescence Recovery After Photo-bleaching) or FLIP (Fluorescence Loss In Photo-bleaching) is proposed, in which a specimen is partly bleached out and a recovery of the bleached portion of the specimen is observed in an observation field with use of a fluorescence observation so that a substance transfer in a cell can be observed. An another observation method is also proposed, in which illumination light rays, i.e., UV light rays are partly applied to a specimen dyed with a caged chemical reagent in which a chemical activities are confined, a characteristic in the part of the specimen is recovered, and a diffusion of the specimen part is observed. In these methods, it is required for the fluorescence observation that an illumination spots or spot on the specimen, in the observation field, are adjustable in size and shape.
In the method of illuminating a part of the specimen in the observation field, a pinhole or a slit are removably arranged at the position of the field stop, which corresponds to the conjugate position in respect of the specimen, so as to realize a partial illumination.
An iris stop is generally used as the field stop, which is provided with a variable aperture having a diameter mechanically and automatically adjusted. This optical arrangement is disclosed in Laid-open Japanese Patents 7-134250 and 2000-502472, in which a liquid crystal device (LCD) of a transmission type is arranged at the position of the field stop and its transparent area is controlled as the variable field stop. According to this arrangement, it is possible to match an illumination region with an observation region, and also illuminate a part in an observation field with a spot of arbitrary size and shape.
However, in this arrangement using the liquid crystal stop, there are problems that the transmission factor of the liquid crystal stop is low even in a state of 100% transmission illumination control, the illumination light level cannot be sufficiently increased, and the color balance of the light rays transmitted through the liquid crystal stop is changed. Thus, the observation precision is lowered. Furthermore, in the case of using UV light rays for fluorescence illumination, it is difficult to prepare a liquid crystal stop having a high UV transmission factor and fluorescence light of low self-emission characteristic.
In addition, the liquid crystal stop has a control response speed, which is as slow as tens of milliseconds. Therefore, if changes in a cell are observed, in relation to an elapse of the time, while changing an illumination position and shape in the observation field, it is difficult to achieve highly precise observation due to such a slow response speed.
In Laid-Open Japanese Patent 2000-502472, a digital mirror device (DMD) is disclosed, which is used instead of a LCD and has a light modulation structure instead of a LCD. However, in the description of the embodiment of this disclosure, there is no concrete description of an arrangement constituting an illumination device with using a DMD.
As described above, the conventional microscope system provided with the liquid crystal stop cannot achieve a sufficient observation precision, because the liquid crystal stop has a low transmission factor, the color balance of transmitted light rays varies, and a response characteristic of a control system is bad.